The invention disclosed herein is based on a state of the art which is known from German OS No. 33 04 980 (which corresponds to copending application Ser. No. 816,946, filed on Jan. 6, 1986, which is a continuation application of Ser. No. 576,672, filed Feb. 3, 1984, now abandoned, and is assigned to the same assignee as the present invention). With this apparatus it is possible to quickly machine hardened gears or those of a hard material, and a high surface quality and a high tooth-system quality is assured.
The term "abrasive surface" means a chip-removing surface of the tool that does not have any uniformly directed cutting edges or the like. This includes all tools having a granular working surface, for example grinding tools, however, also tools for electrolytic or electroerosive or electrochemical material removal. (This does not include for example toothed shaving tools.)
The known apparatus operates in such a manner that only one side of the tool teeth contacts the opposing flank of the workpiece teeth. On the other tooth side there exists a backlash spacing. The contacting tooth side can be changed during the machining operation. The guide gears can run without backlash. However, it is preferable, especially if the tool is moved by changing the center-distance between the tool and the workpiece, to let the guide gears also run with backlash, namely, in such a manner that, referred to the workpiece-tool pairing, the opposite tooth side is in contacting relation. In this manner it is achieved that both the workpiece-tool pairing and also the guide gear pairing operate with backlash, however, the entire gearing arrangement is without backlash. The known apparatus works practically without longitudinal feed. It is possible to use in place of the guide gears friction wheels or friction disks or the like, the manufacture of which is relatively simple. Care must be taken to assure that they have the correct translation characteristic therebetween.
In the known apparatus, only one single place is provided for the workpiece-tool pairing and for the guide gear pairing, at which place the vertically spaced axes cross and this is called the crossed-axes point or the common normal. A specific position or location for the crossed-axes point is not prescribed, namely, it can lie within the tooth width of the workpiece or the guide gear or outside of the tooth system, for example between the mentioned gears; it remains, however, that through this common crossed-axes point the design of the apparatus has limits. Also the tool or a guide gear or both can become very complicated. If, for example, the crossed-axes point lies within the workpiece-tool pairing, then the tool is relatively simple, the guide gears are, however, very complicated, because they must be a combination of a gear for crossed-axes and a bevel gear.
The basic purpose of the invention is to provide an apparatus which can be designed simpler, which can be reset simpler and in which the tool or/and the guide gears are simpler.
This purpose is inventively attained by providing an apparatus of the type described above in which the tool workpiece pairing and for a guide-gear pairing there is provided for each a separate crossed-axes point (common normal).
The invention can be further developed advantageously by providing between the workpiece-tool pairing and the guide gear pairing an interchangeable gear set.
In order that--while maintaining the separate crossed-axes points--both the workpiece-tool pair and also the guide-gears and the interchangeable gear set are well accessible from a servicing standpoint, the invention is preferably constructed so that the workpiece and the gear of the guide gearing that is coupled with the workpiece are arranged on shafts with parallel axes and which are connected to one another through a master gear set. Further, the tool and the gear of the guide gearing that is coupled to the tool can also be arranged on shafts with parallel axes and which are connected through an interchangeable gear set. A simplification results by fixedly installing the master gears in the apparatus.
The inventive apparatus can be simplified in its manufacture when the gears of the guide gear pairing are cylindrical spiral gears. This construction has a favorable effect on the expenses. Since the guide gears have a separate crossed-axes point which is independent of the workpiece-tool pairing, its tooth system can be manufactured independent1y from the shape or form of the tool tooth system.